Haem 4 Flashcards
Normal range of red cells
3.5-5 X 10^12 PER LITER
How many Hb for each red cell
640 mill
Why is haemaglobin found in RBC
Very toxic (free radicals)
Normal Hb
120-160g/L
Molecular weight of Hb
64 kDa
Percentage of heamoglobin synthesised st each stage
65% erythroblast
35% reticulocyte
Which area haem and globin made made in cell?
Haem mitochondria
Globin ribosome
How does iron arrive at the cell
Transferrin (taken up by endocytosis)
Name an important enzyme in the mitochondria in haem synthesis
ALAS (combinng glycine, B6 and Succinyl CoA to begin making haem).
The proto-porphyrin in combined with iron within the mitochondria to make 4 haem, which are then combined with globin chains to make the haemoglobin
Note that Hb must be made in the erythroblast/reticulocyte, as no mitochondria exist in the mature RBC.
Where else contains haem other than haemaglobin
Myoglobin, cytochrome, peroxidases, catalases, tryptophan
What ion state is iron usually in haem
FE2+ ferrous
What is the structure of haem
Protoporyphin ring and central iron atom= (ferroprotoporphyrin)
Why is ALAS important
It is the enzyme by which rate of synthesis is controlled- negative feedback on this enzyme
T/f same globin chains combine with haem
F
Which chains are in the alpha and beta cluster of globin chains…. which chromosome
Beta on 11 (epsilon, gamma and delta and beta)
Alpha on 16 (alpha, zeta)
Both on short arm
When are zeeta chains produced
0-8 weeks
What’s the predominant beta chain cluster during embryologival development
The gamma one (produced until 2 years)
If there is a total inability to produce alpha chains, or beta chains, at what point would this become important and why
From A cluster, alpha and zeta chains produced until 8 weeks. If alpha chains couldn’t be produced, then there would be death in utero after 8 weeks when zeta gene production is switched off
With the Beta cluster, gamma chain is produced until 18 weeks but it decreases from around 8 weeks and beta is supposed to increase. You would notice b-thal at abotut 4-6 months.
Composition of normal adult haemoglobin
HbA (2a 2b) 96-8%
HbA2 (2a 2d) 1.5-3.2%
HbF (2a 2g) 0.5-0.8%
How many AA in each cluster
alpha chain globin 141 AA
all other chains (incl. zeeta) 146AA
Secondary structure of globin
75% of the globin chains adopt helical arrangement (for alpha and beta)
Teritairy structur
Approximate sphere
Hydrophilic surface (charged polar side chains), hydrophobic core
Haem pocket
What is p50
The partial pressure at which Hb is half saturated (usually 26 mmHg)
What shifts curve to left and right
RIGHT: High 2,3-DPG High H+ High CO2 HbS
LEFT:
Left shift (give up oxygen less readily)
Low 2,3-DPG
HbF
Depends on (right)
- H+ ion concentration
- 2,3-DPG synthesis
- CO2 in RBCs
- Hb structure
left:
1. HbF
2. Low 2,3-DPG
What are haemoglobinopathies
Structural variants of Hb or
defects in globin chain synthesis (thal)
What is thalassaemia
when is it suspected
Genetic disorders charwctised by defect in beta globin gene(s) leading to reduced or absent production of globin chains
Suspect when there is microcytosis, anaemia and hypochromic cells IN THE ABSENCE OF IRON DEFICIENCY
What occurs in beta thalassaemia and where is this prevalent
Mutation/deletion of beta chain leading to Reduced or absent production of b globin chains
Prevalence – mainly Mediterranean countries (Greece, Cyprus, Southern Italy), Arabian peninsula, Iran, Indian subcontinent, Africa, Southern China, South-East Asia
Outline beta thalassaemia inheritance
Autosomal recessive
In what case would you get: thalassaemia minor (=trait), thalassamia intermedia thalassaemia major
Beta thal maj.… if you have 2 X Beta zero
Beta thal interm… if you have no copies of normal beta apart from 2 X beta zero (i.e. b+b0, b+b+)
Beta thal min… if you have a copy of a normal beta chain (i.e. bb+, bb0) Inheritence of 1 beta 0 and 1 beta+ (or 2 beta+) will give thalassaemia intermedia which is clinically milder
What could the crossing of beta, beta plus and beta, beta naught patients produce
Which combination of beta chain produced
Beta thal maj
Beta thal intermedia
Betal thal min (=trait)?
25% normal, 25% intermedia and 50% carrier
How can lab diagnosis for beta thalassaemia
Is alpha thalassaemia detected by EPS?
FBC- microcytic hypochromic indecies and increased RBC to HB (reduced MCH and MCHC)
Film- target cells, poikilocytes but no asinocytosis
Hb electrophoresis-
ALPHA: Normal HbA2 and HbF, with or without HbH (tetramer of beta chains)
BETA: Little/no HbA, Raised HbA2 and HbF (normal alpha chains, so delta and gamma chains increased instead of beta and bind to the alpha chains!)
Globin chain synthesis and DNA studies - genetic analysis and looking for mutations like Xmnl polymorphism (in b thal). and a thalassaemia genotype (in all cases)
BECAUSE ALPHA THAL HAS NORMAL HbF/HbA2, you can’t really detect on EPS, so you have to sequence or do genetic analysis
What is thalassamia major,
2 abnormal copies of beta globin gene… sever anaemia not compatible with life, clinical presentation after 4-6 months
How does beta thalassaemia major look on slide
and
how does beta thalassaemia trait look
Major: show extreme hypochromia, microcytosis and poikilocytosis.
Often Howell Jolly bodies and nucleated RBC’s will be present as a result of splenectomy and a hyper plastic bone marrow. Pappenheimer bodies and alpha chain precipitates
Trait: microcytosis, hypochromia and occasional cells showing basophillic stippling
Clinical presentation of beta thal
Management of beta thalassaemia
Presentation: 4-6months. Severe anaemia; hepatosplenomegaly; blood film with hypochromia, poikilocytosis and NRBCs, erythroid herperplasia and extramedullary haematopoiesis.
Refular transfusions 2-3 units per month, become iron overloaded unless treated with iron chelators.
Causes of death in beta thal.
Cardiac failure and infection due to iron overload
Iron overload due to: major multiple blood transfusions, ineffective erythropoiesis and increased gastrointestinal iron absorption lead to iron overload in the body
Thal major treatment
Regular blood transfusion and iron chelation therapy
Splenectomy
Supportive medical care
Hormone therapy (due to infiltration in the ant. Pituitary)
Hydroxyurea to boost HbF
Bone marrow transplant
Outline transfusions
Phenotyped cells,
Aim for pre transfusion Hb of 96-100g/L
Each 2-4 weeks
If high requirement, consider splenectomy
How is infection managed and why is there increased infection risl
Yersinia and other Gram negs because these bacteria thrive on high iron
give prophylaxis in splenectomised patient (immunisation and antibiotics)
When does iron chelation treatment start and what must happen first
After 10-12 transfusion, when ferritin>1000mcg/l
audiology and ophthalmology screening before starting
Drug used to treatment iron chelation
Desferrioxamine (Desferal) - SC
Deferiprone (Ferriprox)
Oral
Deferasirox (Exjade)
oral
SE of deferasirox
rash, GI symptoms, hepatitis, renal impairment
So measure
Side effects of deferiprone (oral) and desferrioxamine
Deferiprone: GI disturbance, hepatic impairment, neutropenia, agranulocytosis, arthropathy
Desferrioxamine: vertebral dysplasia, pseudo-rickets, genu valgum, retinopathy, high tone sensorineural loss, increased risk of Klebsiella and Yersinia infection POOR COMPLIANCE
How can iron overload be monitored
Serum ferritin
(but not that reliable as an acute phase protein)… check 3 monthly if transfused and otherwise anually
liver biopsy (rare) and
T2 cardiac and hepatic MRI
or
ferriscan (R2 MRI)
What is HbH
When three alpha genes are affected…
If 4 affected then death at embryo
you get tetramers or dimers of beta globin chains
What causes right shift on ODC
High 2,3-DPG
High H+
High CO2
HbS
What causes left shift on ODC
Low 2,3-DPG
HbF
What may be seen on slide of someobody being treated for beta thal major
pappenheimer bodies (iron deposits) may be seen as coars blue granules in the RBCs due to iron overload from transfusion
and a chain precipitates (which cause cell to be more rigid and give beta thal. its haemolytic component)
Clinical presentation of thal major
Severe anaemia usually presenting after 4 months
Hepatosplenomegaly
Blood film shows gross hypochromia, poikilocytosis and many NRBCs
Bone marrow - erythroid hyperplasia
Extra-medullary haematopoiesis (leading to thickening of maxillary bones and frontal bossing)
Clinical features of beta thal
Chronic fatigue Failure to thrive Jaundice Delay in growth and puberty Skeletal deformity Splenomegaly Iron overload
Complicatins of beta thalassaemia
Cholelithiasis and biliary sepsis
Cardiac failure
Endocrinopathies
Liver failure
What is sickle beta thalassaemia
They have mutations that cause sickled shaped RBCs (due to mutation in beta chain) and and a second that is associated with beta thalassemia, a blood disorder that reduces the production of hemoglobin
What is HbE beta thal?
haemoglobin E (HbE) is an abnormal hemoglobin with a single point mutation in the β chain…. this alone is classed as mild form of beta thal.
this can be combined with beta thalassaemia
gives beta thalassaemia intermedia or up to b thal major
What is a thalassaemia and what does it result in
Deletion or mutation in a globin gene(s)
Reduced or absent production of a globin chains
affects both foetus and adult!
Note that in a thal, there is reduced HbA2 but in b thal there is increased HbA2
What is HbH and Hb Barts
In a-thal, Excess beta and gamma chains form tetramers of HbH and Hb Barts respectively
What may a thalassaemia carrier experience
Also known as Thalassaemia minor / trait
Carry a single abnormal copy of the beta globin gene
Usually asymptomatic
Mild anaemia
Proble,s associated with thal treatment in developing coutnreis
Lack of awareness of the problems
Lack of experience of health care providers
Availability of blood
Cost and compliance with iron chelation therapy
Availability of and very high cost of bone marrow transplant
T/F RBCs have no nucleus but do have mitochonidra
F- no mitochondria either
Where are globin chaiins produced before 6 weeks, between 6 weeks to about 2 yo, and from just before birth to end of life
yolk sac,
liver and spleen
bone marrow
Reason for removal of spleen in beta thal
extramedullar haematopoesis may lead to splenomegaly…. this can worsen anaemia due to pooling of blood and sequestering of RBCs
What is HbH and Hb Barts
HbH= tetramers of beta chains in alpha thalassaemia
Hb Barts= tetramers of delta chains in alpha thal.
